Fluted liners for shaped charges

ABSTRACT

1. In a spin stabilized shaped charge projectile, a hollow cylindrical casing, means closing the rear end of said casing and a driving band secured thereabout, a high explosive charge filling said casing and having a generally conical cavity in its forward end, a generally conical liner contiguous with said cavity and closing the forward end of said casing, there being a plurality of circumferentially spaced identical flutes on and integral with the walls of said liner, each said flute comprising a generally radially offset surface and a canted surface merging into the next adjacent offset surface, said offset surface facing in the direction of rotation of said projectile, each said offset surface lying in a plane making an angle theta with its respective radial plane and parallel with the axis of said liner.

Elited i Pugh et a1.

tes atet 1 [451 Apr. w, 1973 154] FLUTED LINERS FOR SHAPED CHARGES [73] Assignee: The United States of America as represented by the Secretary of the Army [22] Filed: Aug. 23, 1950 [21] App1.No.: 180,981

554,833 7/1943 Great Britain ..102/56 Primary Examiner-Verlin R. Pendegrass Attorney-J-Iarry M. Saragovitz, Edward J. Kelly and Herbert Berl EXEMPLARY CLAIM 1. In a spin stabilized shaped charge projectile, a ho]- low cylindrical casing, means closing the rear end of said casing and a driving band secured thereabout, a high explosive charge filling said casing and having a generally conical cavity in its forward end, a generally conical liner contiguous with said cavity and closing the forward end of said casing, there being a plurality of circumferentially spaced identical flutes on and integral with the walls of said liner, each said flute comprising a generally radially offset surface and a canted surface merging into the next adjacent offset surface, said offset surface facing in the direction of rotation of said projectile, each said offset surface lying in a plane making an angle 0 with its respective radial plane and parallel with the axis of said liner.

4 Claims, 4 Drawing Figures PATEHTEQAFR I 01373 gwwzmlova 3311121 5011 M- Pugh Ruber c nLEichelbergep .%Z,a% awzw FLUTED LINERS FOR SHAPED CHARGES This invention relates to shaped charges, that is, to explosive charges whose power of penetration of armor plate depends upon the Monroe effect. More particularly the invention relates to a method of and means for effecting material improvement in the penetrating power of shaped charges used in rotating projectiles.

The great penetrating power of the jets produced when a shaped charge is statically detonated at an optimum stand-off distance from protective armor, is well known. It is equally well known that due to conservation of angular momentum of the liner such penetrating power is deleteriously affected when the charge is rotating or spinning, as is the case when it is fired from a rifled gun. For this reason, when maximum penetration was desired, it was heretofore deemed necessary to use such charges with projectiles of the non-rotating type, such as rockets or mortars. On the other hand, the use of such projectors seriously limits the utility of shaped charges because of the inferior accuracy and range as distinguished from spinning projectiles fired from rifled guns. When used in rifled weapons, it has heretofore been necessary to employ velocities materially less than the full velocities of such weapons, resulting in decreased range and accuracy, in order to minimize the deleterious effects of spin.

It is therefore a principal object of our invention to provide a liner for shaped charges which will effectively neutralize or obviate the aforesaid deleterious effect of rotation upon the penetrating power of the shaped charge jet, thereby enabling highly effective use of shaped charge projectiles in rifled weapons, without limitation of their muzzle velocities.

Or, stated in another way, it is a principal object of our invention to provide a liner for shaped charges which will give substantially as good penetrating power to the shaped charge jet with a rotating projectile as that possessed by a like charge when statically detonated.

A second principal object is the provision of an improved method for effecting greater penetration by rotating shaped charges than has heretofore been possible.

More specifically, it is a purpose of the invention to provide a fluted liner for shaped charges wherein the detonation of the charge itself coacts with the flutes of the liner to apply a net torque thereto about the axis of spin sufficient and in direction to oppose and substantially nullify the angular momentum of the spinning liner and thus result in a penetration comparable to or equal to that of a statically detonated charge of like composition, quantity and shape.

A further object is to provide a fluted lining for a shaped charge wherein the increments of net torque resulting from the detonation of the charge, for each section of the lining of like axial dimension, will not vary greatly, whereby the lining will collapse uniformly and give a penetration comparable to a like statically detonated charge.

Other objects and advantages will be apparent from a study of the following specification in connection with the accompanying drawing.

In the drawing:

FIG. 1 is a broken axial section showing a projectile casing and shaped charge equipped with a liner constructed according to the invention,

FIG. 2 is a cross section on line 2-2, FIG. 1 and to an enlarged scale, of a portion of the fluted liner,

FIG. 3 is an axial cross section of a portion of the liner of FIGS. 1 and 2, wherein the depth of the flutes vary linearly with distance from the apex of the liner, and

FIG. 4 is an axial cross section corresponding to FIG. 3 but showing a modification wherein the depth of the flutes vary non-linearly with distance from the apex of the cone.

Referring in detail to the drawing, and particularly to FIG. 1, the numeral 1 identifies a projectile casing having its rearward end closed by a plug or adapter 2 shaped to receive a base fuze 3 of any well-known type and having an associated booster 4 within the main charge 5.

The forward end of the casing is closed by a generally conical liner 6 fitting a correspondingly-shaped cavity or depression in the explosive charge 5. This liner may be held in position by any suitable means such as light ogi'val nose cap or windshield, not shown, secured to the forward end of casing 1 to close the same. The liner may be formed from sheet metal such as copper, aluminum, steel, or other suitable material and is formed with a number of flutes (16 in the model illustrated) equally circumferentially spaced. Each flute comprises an abrupt offset 7 joined to the next adjacentoffset by a canted surface 8. The offset surfaces 7 may be in respective radial planes through the axis of the cone, or each may lie in a plane making an angle 0 with its respective radial plane and parallel with the axis. The angle 0 may be varied within reasonable limits. Each offset surface extends parallel with an element of the cone at that location and varies in depth or radial component with distance from the apex. The variation may be linear or non-linear. In the latter case, the rate of increase of flute depth increases from apex to base of the cone. FIG. 4 illustrates such a liner 9 having flutes 10 which increase in depth at an increasing rate from apex to base. The outside surfaces face in the direction in which the projectile rotates under the angular momentum imparted by the gun. Thus the cones shown are for use with guns in which the rifling is counterclockwise, looking from breech to muzzle.

In operation, when the charge explodes the detonation wave imparts rotational forces to the liner. Its effect upon the offset surfaces 7 of the flutes tends to cause clockwise rotation while its effect upon the canted surfaces tends to cause counterclockwise rotation. However, we have found that the sum of the forces exerted upon the offset surfaces predominate over the sum of those exerted upon the canted surfaces with the result that a net clockwise rotational impulse is thus applied to the cone. This net impulse may be regulated by varying the number, depth, and angle of the offset surfaces, among other factors, so that angular momentum of the liner is substantially nullified in response to detonation of the charge, and the penetrating power of the jet closely approximates that of a statically fired charge of like size and design, but provided with a liner of conventional design.

While the criteria determining the number, depth, and rate of change of depth of the offset flute surfaces of any liner, will vary widely with the conditions of use, such as range and muzzle velocity of the projectile, in a typical case, the caliber of the gun and the usual ranges at which it is fired, as well as the rotational speed of the projectile corresponding to those ranges, will be known. The problem, then, becomes one of effecting substantially complete compensation, that is, nullification of the effects of angular momentum over the desired range of rotational speeds, in response to detonation of the shaped charge, by pre-selection of the number of flutes and then determining the required depth and contour of the offset fluted surfaces to effect the desired compensation over the specified range of rotations. In making a proper selection, it is important to bear in mind that since detonation pressures and collapse velocities are different for each element of the liner, each zone of the liner should fully compensate for or overcome, its own angular momentum. It is for this reason that the non-linear modification of FIG. 4 may be provided. However, since the impulse imparted by the offset surfaces varies with the sharpness of the flutes, being greater with sharp edges, it may be possible to achieve substantially uniform neutralization or compensation for each section of the liner, but offset surfaces which vary in depth linearly with distance from the apex, and in which the component compensating impulses from section to section of the liner have the desired non-linear variation by reason of rounded edges of the flutes. Indeed, the rates of change may conceivably be increased by varying the flute edges from well-rounded adjacent the apex to sharp at the base. In all cases, of course, the flutes of a given liner should be identical in size and shape.

While it is obvious from the foregoing that the shape, number and depth of flutes and other characteristics of a liner, to effect substantially complete compensation over any range of rotational speeds, may vary widely, we have effected substantially complete compensation at a rotational speed of 150 r.p.s., to effect a maximum penetration not materially less than that of the best liners of conventional form fired statically, using copper cones having 16 flutes with a maximum flute depth of 0.025 inch, an apex angle of 42 and a wall thickness of 0.045 inch. Similarly, by suitable changes of liner design, substantially complete compensation has been effected at rotational speeds up to 350 r.p.s.

Certain terms and expressions as used in the appended claims, are to be interpreted as follows:

the expression generally conical includes liners of trumpet shape, that is, liners which flare outwardly from apex to base and in which the elements are curves rather than straight lines. The expression also includes liners of other regular shapes whose contour is defined by curved or straight elements, e.g. hemispherical, paraboloidal, hyperboloidal, compound conical, etc.;

the central axis of the liner is the axis of symmetry thereof;

the elements of the liner are lines in the surface thereof cut by planes passing through the central axis of the liner;

the exterior surface of the liner is to be interpreted as that surface in contact with the explosive charge in the assembled projectile.

It will thus be realized that we have provided a liner for shaped charges which will enable the charges to be fired from rifled weapons, with the usual high velocity, accuracy and range and which, at the same time, will be capable of a maximum penetration substantially as great as like charges lined with smooth cones and fired statically.

While we have disclosed the preferred form of the invention as now known to us, various modifications have been suggested herein. Others will readily occur to those skilled in the art after a study of the foregoing disclosure. For this reason, we do not desire to be limited to the precise details of construction shown but desire that the disclosure be taken merely in an illustrative sense. It is our desire and intention to reserve all such changes and modifications as fall within the scope of the subjoined claims.

We claim: I

1. In a spin stabilized shaped charge projectile, a hollow cylindrical casing, means closing the rear end of said casing and a driving band secured thereabout, a high explosive charge filling said casing and having a generally conical cavity in its forward end, a generally conical liner contiguous with said cavity and closing the forward end of said casing, there being a plurality of circumferentially spaced identical flutes on and integral with the walls of said liner, each said flute comprising a generally radially offset surface and a canted surface merging into the next adjacent offset surface, said offset surface facing in the direction of rotation of said projectile, each said offset surface lying in a plane making an angle 0 with its respective radial plane and parallel with the axis of said liner.

2. The combination recited in claim 1 each said flute comprising a radially offset surface having a depth varying linearly with distance from the apex of said liner, the line formed by said canted surface and contingent offset surface forming a sharp edge at the base of said liner which is gradually rounded from base to apex.

3. In a shaped-charge spin-stabilized projectile having a hollow cylindrical casing, a high explosive charge in said casing having a generally conical cavity in its forward end, a generally conical liner contiguous with said cavity and closing the forward end of said casing, said liner having a fluted surface from the apex to the base thereof in contact with said explosive, each of said flutes comprising a short, generally radial abrupt offset surface adjoining a longer canted surface, said abrupt offset surfaces facing in the direction of rotation of said projectile to nullify the effect of said rotation on said liner by diverting a portion of the energy of said charge into a rotational impulse on said liner opposite in direction to the spin of said projectile.

4. In a spin-stabilized projectile having a hollow cylindrical casing, means on said projectile for imparting spin to said casing, a high explosive charge in said casing having a generally conical cavity in its forward end, a generally conical liner contiguous with said cavity and closing the forward end of said casing, the surface of said liner in contact with the charge being provided with a series of similar short offset surfaces oriented along generally radial planes extending from the apex to the base of said liner, each of said offset surfaces facing in the direction of spin of said projectile and joined to the next succeeding offset surface by a relatively long gently canted surface, the configuration of said liner diverting a portion of ,the energy of the charge into a rotational impulse on said liner opposite in direction to the spin of said casing. 

1. In a spin stabilized shaped charge projectile, a hollow cylindrical casing, means closing the rear end of said casing and a driving band secured thereabout, a high explosive charge filling said casing and having a generally conical cavity in its forward end, a generally conical liner contiguous with said cavity and closing the forward end of said casing, there being a plurality of circumferentially spaced identical flutes on and integral with the walls of said liner, each said flute comprising a generally radially offset surface and a canted surface merging into the next adjacent offset surface, said offset surface facing in the direction of rotation of said projectile, each said offset surface lying in a plane making an angle theta with its respective radial plane and parallel with the axis of said liner.
 2. The combination recited in claim 1, each said flute comprising a radially offset surface having a depth varying linearly with distance from the apex of said liner, the line formed by said canted surface and contingent offset surface forming a sharp edge at the base of said liner which is gradually rounded from base to apex.
 3. In a shaped-charge spin-stabilized projectile having a hollow cylindrical casing, a high explosive charge in said casing having a generally conical cavity in its forward end, a generally conical liner contiguous with said cavity and closing the forward end of said casing, said liner having a fluted surface from the apex to the base thereof in contact with said explosive, each of said flutes comprising a short, generally radial abrupt offset surface adjoining a longer canted surface, said abrupt offset surfaces facing in the direction of rotation of said projectile to nullify the effect of said rotation on said liner by diverting a portion of the energy of said charge into a rotational impulse on said liner opposite in direction to the spin of said projectile.
 4. In a spin-stabilized projectile having a hollow cylindrical casing, means on said projectile for imparting spin to said casing, a high explosive charge in said casing having a generally conical cavity in its forward end, a generally conical liner contiguous with said cavity and closing the forward end of said casing, the surface of said liner in contact with the charge being provided with a series of similar short offset surfaces oriented along generally radial planes extending from the apex to the base of said liner, each of said offset surfaces facing in the direction of spin of said projectile and joined to the next succeeding offset surface by a relatively long gently canted surface, the configuration of said liner diverting a portion of the energy of the charge into a rotational impulse on said liner opposite in direction to the spin of said casing. 